This invention relates to an optical axis adjustment method of adjusting an optical axis of an optical fiber to a beam axis of an optical element, such as a semiconductor laser device, a light emitting diode, or the like.
In general, it often happens that an optical element and an optical fiber are assembled into an optical module in order to transmit a light beam from the optical element through the optical fiber. In this event, an optical axis of the optical fiber must be precisely aligned with or adjusted to a beam axis of a light beam emitted from the optical element. Such adjustment of an optical axis to a beam axis should be made three-dimensionally and rotatably around the optical axis of the optical fiber. Otherwise, a maximum quantity of light can not be transmitted through the optical fiber.
Taking the above into consideration, the optical fiber and the optical element are relatively moved in a three-dimensional coordinate, for example, an orthogonal coordinate of x-y-z. In addition, the optical fiber is rotated around the optical axis thereof relative to the optical element to adjust the rotational angle of the optical fiber to that of the optical element.
At any rate, the adjustment of the optical fiber to the optical element is accomplished by monitoring a maximum quantity or value of the light beam emitted from the optical fiber. The quantity or value of the light beam emitted from the optical fiber may be also referred to as a light power value.
More specifically, a maximum value emitted from the optical fiber is detected along each of an x-axis, a y-axis, and a z-axis and rotatably around the optical axis of the optical fiber, when the optical axis of the optical fiber is adjusted to the beam axis of the light beam emitted from the optical element. To this end, a measured value measured at a certain position of the optical fiber is compared with another measured value measured at another position shifted from the certain position by a predetermined pitch. Thereafter, the maximum measured value is selected from the measured values. Similar operation is successively repeated to detect the maximum value of the light beam along each of the x-, the y-, and the z-axes and around the optical axis of the optical fiber. As a rule, such operation may be called a hill-climbing method.
However, when an actual maximum position at which the maximum value is measured is very far from a current position, the comparisons should be repeated many times. This shows that a very long time is taken to search for the maximum value of the light beam along each axis and around the optical axis.